Downflow stability arrangement



Smut. 7, 1965 E. W. BENSON 3,204,612 DOWNFLOW STABILITY ARRANGEMENT Filed April 16, 1964 74 @6 2 27 V Z6 f a 33 PRESSURE SOURCE "13 PRESSURE 3/ V F SOURCE 35- r 36 United States Patent a 3 204,612 DOWNFLDW STAIHLITY ARRANGEMENT Elliot W. Benson, Mount Vernon, N .Y., assignor to Foster Wheeler Corporation, New York, N.Y., a corporation of New York Filed Apr. 16, 1964, Ser. No. 360,185 9 Claims. (Cl. 122-406) This invention relates to vapor generators. It is a continuation-in-part of my patent application, Serial No. 215,740, now abandoned which was filed on August 8, 1962.

In particular, this invention relates to a multiple tube downflow vapor system contained within a superheat region of a boiler and having variable orifices operable by means of a single slide member.

The downflow system of the present invention may be found in a heated region which comprises many tube passes both up and down. More specifically, the present invention refers to a radiant superheater section where a downflow pass is often used in conjunction with an upflow pass. The present advance may also be used in a once-through boiler.

In a multi-tube downflow portion of a superheat cycle, two problems can be encountered; one, non-uniformity of flow among the various downflow tubes, thereby presenting an overheating problem in those tubes with a reduced flow; and, two, reverse flow, or, upflow. Variations in total vapor flow through the downflow system as a whole substantially affect system friction head loss. In multiple tube systems that have low friction head loss, the probability of flow variations among the various tubes is increased. At high flow, friction is generally ample and flow is generally uniform; but at low flow, friction may be inadequate to produce uniform flow. Upfiow vapor tube systems are relatively stable and the above problems inherent in downflow sections are comparatively reduced.

In downflow sections, the gravity head hinders the flow. Assuming no head loss, the pressure at the lower header due to gravity, is greater than the pressure at the upper header. In an upflow section, gravity tends to make the pressure at the inlet greater than the pressure at the outlet, reducing the possibility of reverse flow. In downflow systems, it is essential that the friction head be maintained greater than the gravity head to insure downflow.

To maintain downflow in downflow systems and reduce flow variations among the tubes at low flow rates, fixed flow throttling devices have been introduced into downcomer systems to constrict the tubes and increase the friction head so that uniform flow is present among the tubes. However, when high flow occurs, devices of this type can cause excessive friction head and consequent power loss.

The present advance contemplates a variable ganged throttling device operated by a unique control means. A plate throttle is disposed in the upper header of a downflow system. The throttle defines uniform ports registrable with the tube ends. Control means continually responsive to the pressure between the upper and lower headers moves the throttle longitudinally relative the upper header to adjust the degree of registry of the ports with the tube ends. "Friction head loss is automatically adjusted and is optimized within a wide range of operating flow conditions thereby insuring uniform downflow among the tubes. Adequate cooling is maintained for all tubes; execessive friction head loss is avoided. Reliability is enhanced by simple rugged design utilizing a piston to move the throttle.

The same advance may be used in upflow systems.

3,294,612 Patented Sept. 7, 1965 The above and other advantages will appear more fully from the accompanying drawing wherein:

FIGURE 1 is an elevational view in section of a down flow system according to the present invention;

FIGURE 2 is a fragmented elevation view in section on an enlarged scale illustrating a portion of the control means for operating the throttle; and

FIGURE 3 is an enlarged fragmented isometric projection taken through the upper shell and showing the relationship of the throttle with the tube ends.

In the drawing the downflow system includes upper header 1 and lower header 2 with a plurality of tubes 3 connected vertically therebetween. In this system a vapor is conducted via the interior 4 of the upper header through openings 6 which communicate with. tube ends 7.

Throttling is employed to vary friction through this downflow system. A throttle is shown as plate 8 disposed in header 1 near inside wall 9 about tube ends 7. Plate 8 defines ports 11, each of which are registrable with a tube end 7. Ports 11 need not be circular as here shown.

Control means comprising piston 26, pressure chamber 29, valve 32, pressure source 36 and pressure controller 35 shown in FIGURES 1 and 2 are provided for moving plate 8 relative tube ends 7 adjusting the degree of registry of ports 11 with the corresponding tube ends 7. Piston 26 is adapted to move the plate longitudinally relative cylindrical header 1. As best seen from FIGURE 3 plate 8 includes a pair of longitudinal edges 13 and 14. Retainer ridges 16 and 17 are connected to header 1 laterally of edges 13 and 14 respectively. Retainer ridges 16 and 17 define recesses 18 and 19 facing each other and adapted to receive edges 13 and 14 respectively holding plate 8 therein for sliding movement relative header 1 while plate 8 is juxtaposed to shell Wall 9.

Binding of the plate 8 against header wall 9 is prevented. Side 21 of the plate is disposed adjacent header wall 9 defining clearance 22 therebetween. Passage 23 penetrates header 1 to communicate clearance 22 with a source of pressurized fluid 37 via conduit 24.

As best seen in FIGURE 2, plate 8 is connected to piston 26 for movement therewith. To accommodate such an arrangement, header 1 is machined between stops 27 and 27a at one end to provide a seat for piston 26. Plate 8 has an open position with piston 26 against stop 27 wherein ports 11 are in maximum registry with tube ends 7, and a closed position with piston 26 against inner stop 27a wherein ports 11 are in minimum registry with tube ends 7. A thrust is provided by the inward force of pressure on outside face 28 of piston 26 for moving plate 8 between stops 27 and 27a for changing the degree of registry of ports 11 with tube ends 7. Sensing device 34 (conventional pressure probes connected between the headers) directly and fully responsive to the actual pressure between the headers feeds a signal to pressure controller 35 making the latter directly and fully responsive to the actual difference in pressure between upper header 1 and lower header 2. Valve 32 controlled by pressure controller 35 regulates the pressure. applied to chamber 29 through line 31 from constant pressure source 36. Valve 32 is biased at its intermediate open position so that it may open or close so as to increase or decrease the pressure in chamber 29.

To insure downflow the pressure in upper header 1 must be greater than the pressure in lower header 2, i.e., the friction head must be greater than the gravity head. To insure uniform flow among tubes 3 the pressure difference between upper header 1 and lower header 2 must be maintained sufficiently large relative the variations of the gravity head among the tubes (which is caused by density variations due to temperature differences among the tubes) so that consequently, the variations of the gravity head will have a negligible effect on the flow variations among the tubes. This predetermines a required minimum pressure differential between the upper and lower header. As the actual pressure differential between the headers falls or tends tofall below this minimum value as a result of variations in the gravity head and/ or the friction head due to flow, pressure controller 35, responsive to sensing device 34, actuates valve 32 and causes the pressure in chamber 29 to become greater than the pressure in chamber 4. Piston 26 moves plate 8 inward, moving ports 11 further out of registry with tube ends 7 thereby increasing the system friction head. This action continues automatically so that the pressure differential remains or is maintained above the minimum pressure differential value.

The pressure ditferential between upper header 1 and lower header 2 is limited to a predetermined maximum value so that unnecessary pump power is not expended. Between the maximum and minimum pressure values an operational pressure range is defined. As the pressure differential rises or tends to rise above the predetermined maximum value, pressure controller 35 responsive to sensing device 34, actuates valve 32 to cause the pressure in chamber 29 to become lower relative the pressure in chamber 4. Piston 26 moves plate 8 outward, moving ports 11 further into registry with tube ends 7. The friction head is thereby reduced and the pressure differential between the headers returns to or remains within the operational range.

The present advance may be used in upfiow systems to obtain flow uniformity; however, the criteria for the predetermined minimum and maximum pressure values may be different since the gravity head aids the flow. It will be apparent to those skilled in the art that changes may be made in the details of the preferred embodiment without departing from the scope of the invention as defined by the claims.

What is claimed is:

1. A system for a vapor generator comprising a horizontally extending inlet header having an inside wall and an interior,

a horizontally extending outlet header having an interior in approximately vertical spaced relationship to the inlet header,

a plurality of substantially identical tubes connected between said headers,

the inlet header defining a plurality of openings which communicate the interior of the inlet header in flow series with the tubes,

the outlet header defining a plurality of openings which communicate the tubes in flow series with the interior of the outlet header,

a movable throttle disposed in the inlet header juxtaposed relative the inside wall about each of said openings,

the throttle defining ports respectively registrable with each tube opening to pass fiuid between the tubes and the interior of the inlet header,

sensing means directly and fully responsive to the actual difference in pressure between the inlet header and the outlet header,

Control means responsive to the sensing means for positioning the throttle relative the inlet header to adjust the degree of registry of the ports with the openings of said inlet header whereby friction through the system is varied.

2. The system of claim 1 wherein all the ports are positioned to be simultaneously in the same degree of registry with the openings of said inlet header.

3. The system of claim 1, the control means comprising a piston connected at one end to said throttle, said inheader machined to accommodate the piston for sliding engagement therein,

a pressure supply means for supplying a pressure force to the other end of the piston,

a pressure controller means responsive to the sensing means,

a control valve actuated by said pressure controller means for controlling the pressure force supplied to the other end of said piston by said pressure supply means for operatively positioning the throttle relative the inlet header.

4. A downfiow system for a vapor generator comprisa horizontally extending upper header having an inside wall and an interior,

a horizontally extending lower header having an interior in approximately vertical spaced relationship to the upper header,

a plurality of substantially identical downfiow tubes connected between said headers,

the upper header defining a plurality of openings which communicate the interior of the upper header in flow series with the tubes,

the lower header defining a plurality of openings which communicate the tubes in flow series with the interior of the lower header,

a movable throttle disposed in the upper header juxtaposed relative the inside wall about each of said openings,

the throttle defining ports respectively registrable with each opening to pass fluid between the tubes and the interior of the upper header,

sensing means directly and fully responsive to the actual difference in pressure between the upper header and the lower header,

control means responsive to the sensing means for operatively positioning the throttle relative the upper header to adjust the degree of registry of the ports with said openings of said upper header, whereby friction through the downfiow system is varied.

5. A downfiow system for a vapor generator comprising an upper header having an inside wall and an interior,

-a lower header having an interior in approximately vertical spaced relationship to the upper header,

a plurality of downflow tubes connected between said headers,

the upper header defining a plurality of openings which communicate the interior of the upper header in flow series with the tubes,

the lower header defining a plurality of openings which communicate the tubes in flow series with the interior of the lower header,

a movable throttle disposed in the upper header juxtaposed relative the inside wall about each of said openings, said throttle comprising a plate having a pair of longitudinal edges, the plate defining ports respectively registrable with each opening to pass fluid between the tubes and the interior of the up per header,

a ridge connected to the interior of the upper header laterally of each of the edges, each of the ridges defining a recess, the recesses facing each other and adapted to receive the edges thereby holding the plate in longitudinal sliding engagement therebetween,

sensing means directly and fully responsive to the actual difference in pressure between the upper header and the lower header,

control means responsive to the sensing means adapted to operatively move the plate longitudinally relative the upper header in the recesses to adjust the degree of registry of the ports with said openings of said upper header whereby friction through the system is varied.

6. The downflow system of claim 5, the control means comprising,

a piston connected at one end to said throttle, said upper header machined to accommodate the piston for sliding engagement therein,

a pressure supply means for supplying a pressure force to the other end of the piston,

a pressure controller means responsive to the sensing means,

a control valve actuated by said pressure controller means for controlling the pressure force supplied to the other end of said piston by said pressure supply means for operatively positioning the plate relative the inlet header.

7. The downflow system of claim 5 with the plate having a side juxtaposed relative the inside Wall, said side and said inside Wall defining a clearance therebetween, means communicating a fluid pressure to the clearance.

8. The downflow system of claim 7 wherein all the ports are positioned to be simultaneously in the same degree of registry with the openings of said upper header.

9. The downflow system of claim 7 with,

the plate having a side juxtaposed relative the inside wall, said side and said inside wall defining a clear- References Cited by the Examiner UNITED STATES PATENTS 12/06 Tracy 6/ 13 Caille 8/29 La Mont et a1.

5/35 Lucke 8/43 Turner FOREIGN PATENTS 3/30 Great Britain.

FREDERICK L. MATTESON, JR., Primary Examiner.

KENNETH W. SPRAGUE, PERCY L. PATRICK,

Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,204,612 September 7, 1965 Elliot W. Benson It'is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 69, for "in-" read inlet column 5, line 17, for the claim reference numeral "7" read 6 column 6, line 3, after "in" insert the same degree of registry Signed and sealed this 15th day of March 1966.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. A SYSTEM FOR A VAPOR GENERATORE COMPRISING A HORIZONTALLY EXTENDING INLET HEADER HAVING AN INSIDE WALL AND AN INTERIOR, A HORIZONTALLY EXTENDING OUTLET HEADER HAVINGAN INTERIOR IN APPROXIMATELY VERTICAL SPACED RELATIONSHIP TO THE INLET HEADER, A PLURALITY OF SUBSTANTIALLY IDENTICAL TUBES CONNECTED BETWEEN SAID HEADERS, THE INLET HEADER DEFINING A PLURALITY OF OPENINGS WHICH COMMUNICATE THE INTERIOR OF THE INLET HEADER IN FLOW SERIES WITH THE TUBES, THE OUTLET HEADER DEFINING A PLURALITY OF OPENINGS WHICH COMMUNICATE THE TUBES IN FLOW SERIES WITH THE INTERIOR OF THE OUTLET HEADER, A MOVABLE THROTTLE DIPOSED IN THE INLET HEADER JUXTAPOSED RELATIVE THE INSIDE WALL ABOUT EACH OF SAID OPENINGS, THE THROTTLE DEFINING PORTS RESPECTIVELY REGISTRABLE WITH EACH TUBE OPENING TO PASS FLUID BETWEEN THE TUBES AND THE INTERIOR OF THE INLET HEADER, SENSING MEANS DIRECTLY AND FULLY RESPONSIVE TO THE ACTUAL DIFFERENCE IN PRESSURE BETWEEN THE INLET HEADER AND THE OUTLET HEADER, CONTROL MEANS RESPONSIVE TO THE SENSING MEANS FOR POSITIONING THE THROTTLE RELATIVE THE INLET HEADER TO ADJUST THE DEGREE OF REGISTRY OF THE PORTS WITH THE OPENINGS OF SAID INLET HEADER WHEREBY FRICTION THROUGH THE SYSTEM IS VARIED. 